In the installation of utility or transmission lines, the practice of drilling directionally controlled, generally horizontal, boreholes through the earth at generally shallow depths beneath the earth's surface has gained increasing acceptance. The combination of equipment to drill generally horizontal or directional boreholes is built around a downhole drilling motor apparatus, often called a mud motor, which is used for rotating the drill bit which cuts through soil and rock. While the disclosed orienter of the present invention is shown mounted to the downhole end of coiled tubing as shown in U.S. Pat. No. 6,536,539 to the same assignee, it may also be used on the downhole end of a continuous non-rotating string of pipe segments.
To control the direction at which a generally horizontal borehole is drilled for utility line installation, some type of orienter is typically provided to direct the travel of the rotating drill bit along the desired path. Following the desired path may begin by requiring the rotating drill bit to first penetrate the earth's surface at a shallow angle, bore downwardly to a predetermined depth, then level out, then possibly direct the rotating drill bit to turn downward to move deeper, or possibly direct the rotating drill bit to turn to one side to avoid an obstacle, or to move along a more direct path toward a predetermined target, then finally, to turn upward to return back to the earth's surface.
In the art of drilling subterranean, substantially horizontal or directional boreholes with a rotating drill bit powered by a motor and advanced through the borehole by coiled tubing, there typically exists a need to position or direct a fixed bend or angle built into the downhole mounting for the rotating drill bit to facilitate directing the path of the borehole in something other than a straight line.
Various prior art drilling tool assemblies have been developed to cause a rotating drill bit to form a borehole whose path follows something other than a straight line. These prior art drilling tools utilize a variety of technologies to control the direction of the rotating drill bit and thus the path of the completed borehole. Some of the technologies for controlling the direction of the rotating drill bit include: a) pressure activated positioners, which operate independently to index the position of a downhole mud motor having a housing with a fixed bend, to a desired position; b) pressure activated tools which operate independently to create a “kick” or a temporary bend at a specific location, when activated by a predetermined signal; c) activated deflection shoes which independently operate to engage one side or face of the borehole, somewhere behind the cutting face of the rotating drill bit, to push the cutting tool face off to one side; and d) rotary tools which either allow the drilling motor to be rotated to a desired position and then either locked into the desired position or which allow the drill motor to rotate constantly to provide a straight hole and then lock up on command when directional drilling is required. All of the devices which implement these technologies to form a borehole following something other than a straight line are commonly referred to as “orienters.” In addition, prior art orienters typically require a separate source of power and control mechanism for redirecting the mounting apparatus for the rotating drill bit from a configuration which forms a bore hole following a straight line to a configuration which forms a bore hole following something other than a straight line, typically a shallow arc.
Generally, in subterranean shallow depth prior art coiled tubing drilling operations, the drilling tool assembly mounted to the end of a length of non-rotating coiled tubing includes: a rotating drill bit, preceded by a hydraulic motor assembly. The hydraulic motor assembly is typically housed in a long tube. Rotation of the motor is caused by the flow of drilling mud (typically called a “mud” motor). Above the mud motor, closer to the end of the coiled tubing, is a steering tool (or mechanism capable of tracking and reporting on the geometry of the path of the completed borehole). Above the steering tool and generally connected to the end of the coiled tubing is the orienter (a tool capable of changing the direction in which the rotating drill bit is pointed as it forms a subterranean shallow depth borehole). The coiled tubing connected to the orienter provides the linear force at the proximal end of the drilling tool assembly. It is this linear force which moves the drilling tool assembly through the borehole as the rotating drill bit cuts through the soil and rock at the drill face in contact with the rotating drill bit at the distal end of the drilling tool assembly.
The rotating drill bit is turned by the torque provided by the mud motor. The combination of the continuous rotary motion and the hardened projections on the end of the rotating drill bit enable the rotating drill bit to cut through soil and rock and thereby create a subterranean borehole. The mud motor produces the rotary power or torque needed to turn the drill bit by converting the energy from the flow of fluid or drilling mud, which is pumped through the mud motor, into rotary power or torque.
The steering tool, which is typically positioned behind or above the mud motor, provides signals which are used to track the path of the borehole, formed by a combination of straight and arcuate borehole segments.
The orienter portion of the drilling tool assembly is used to provide the necessary physical movements to position the entire drilling tool assembly to alter the path of the borehole by causing the drilling tool assembly to create a straight line segment or to create an arcuate segment.
In some prior art directional drilling systems, the drive shaft portion of the drilling motor is coupled to a swivel type joint or CV type joint at a point in the motor housing which includes a fixed bend. This construction allows for an oscillating rotation of the drive shaft in a conical fashion. Also, common in some prior art drilling tool assemblies, the orienter portion includes an array of thrust bearings and seals to properly displace and transmit the forces which determine the path of the borehole.
The geometry of the combination of the straight and arcuate segments at predetermined locations within the completed borehole is dictated, in part, by the bend in the mud motor housing. To create a straight segment of a borehole, the orienter facilitates either continuously rotating the drill and the bent portion of its mounting, or the orienter periodically moves one or more components in the drilling tool assembly to form an arrangement which will produce a substantially straight borehole segment.
To create an arcuate segment of a borehole, the orienter typically does not allow the bent portion of the drill bit mounting to rotate, thereby enabling the fixed bend portion of the mud motor housing to create an arcuate segment of the borehole. Available orienters for use with drilling tool assemblies feature a multitude of designs and functions. The device disclosed in U.S. Pat. No. 5,215,151, to Smith is illustrative of a drilling tool assembly including a fixed bend.
To monitor the position of the drilling tool assembly and the orientation of the rotating drill bit, a variety of different techniques have been utilized. Some systems utilize radio beacon transmitters located within the steering tool portion of the drilling tool assembly. This is known as a sonde housing. The radio signals from the transmitter in a sonde housing may be received either by using a walkover receiver or by using a wireline which follows the drilling tool assembly into the borehole. The radio signals provide necessary information about the position of the drilling tool assembly and the orientation of the rotating drill bit. Such rotating drill bit orientation information may include: clock face position, pitch, roll, yaw, and azimuth. With the information about the position of the drilling assembly and the orientation of the rotating drill bit, the operator may control the direction of the path of the borehole.
As the sophistication of coiled tubing drilling applications has progressed and new drilling tools are tested and operated, certain procedures have been found to be more conducive to drilling generally horizontal or directional boreholes with coiled tubing. As previously indicated, the drilling of boreholes for the installation of utility or transmission lines typically includes causing the drilling tool assembly to first penetrate the ground surface at a shallow angle, then move to a predetermined depth, then traverse a generally horizontal predetermined path to travel under or around obstacles, and finally to move upwardly to exit the ground surface at a shallow angle some distance away. In such prior art drilling operations for the installation of utility lines, the entire drilling tool assembly (in some cases the rotating drill bit, the motor together with its housing, the steering tool, and the orienter can be as much as ten feet long) must completely exit the ground to be removed from the end of the coiled tubing. Simply because of the extended length of the drilling tool assembly, the process of removing the entire drilling tool assembly from the end of the coiled tubing can be quite cumbersome. Accordingly, it is desirable to develop an orienter for a drilling tool assembly that is simpler in construction, reduces the length of the drilling tool assembly, and reduces the power requirements without detracting from the functionality of the prior art orienters used in drilling tool assemblies.
There remains, therefore, in the art a need for a new system and method to orient a drilling tool assembly which simplifies the construction of the drilling tool assembly, shortens the length of the overall drilling tool assembly, and either minimizes the power required for orientation of the drilling tool assembly or eliminates the need for a separate power source to perform the orienting function.